How to collect all the light emitted from a certain source and further to shape the beam into a desirable form is a well known problem. An ideal solution for many applications would be to image the source by using the rays emitted to one hemisphere about the source. Here the term ‘imaging’ does not mean image forming with minimized aberrations but merely imaging with a sufficient quality for illumination.
One well-known approach is to use high-NA (numerical aperture) objectives, like aspherical pick-up lens systems or microscope objectives. These solutions are either large in respect to the collected etendue, or incapable to form good enough image from the object. These systems may also be complex and expensive. These teachings take a different approach. Instead, embodiments of this invention make it possible to form an illumination quality image of an object by using the rays emitted at large angles to the optical axis of the imaging system (e.g., side-emitted rays).
The light collection problem becomes more difficult if one needs to collect all the light emitted from a source which is inside a material whose refractive index n is larger than that of the surrounding material, typically air (n=1). Typically, large angle collection is possible only if the source is in air. If the source is encapsulated in higher refractive-index material, typical collection optics tends to be too large to be useful. Additionally, many typical optical collection solutions (such as collection lenses, TIR-collimators, tapered lightpipes, parabolic concentrators) only collect light and other components are needed to shape the beam to a desired form such as a uniform rectangle for example. That results in a larger optical system size and additional losses due to the increased number of discrete components or due to increased etendue of the beam. Embodiments of this invention address this problem in that the components described make it possible to form image of an object at large angles even when the object is inside a material with an index of refraction greater than the surrounding material.
In many applications it would be advantageous to have a very low-F-number objective, technically an ultra-high numerical aperture, which need not have perfect imagery but rather a high throughput. Embodiments of the invention address this issue in that the numerical aperture of the components described herein can be equal to the refractive index of the material by which the object to be imaged is surrounded.
There are other design considerations where an object or data needs to be imaged from angles far from the optical axis. For example, in some applications the optical axis is blocked or unavailable for direct imaging due to other uses, and there is also a need to illuminate the object with high throughput. As will be seen below, embodiments of the invention address that problem also.
In miniature LED projection engines, one difficult problem is how to couple the light from the LED chip through a rectangular microdisplay and the projection lens onto the screen. This needs to be done efficiently and in a small space and still provide uniform image quality. Those considerations are fully described and designed for in co-owned U.S. Pat. No. 7,059,728 by enclosing an LED source within an optical medium on one side and a reflecting substrate on the other. Light from the non-point LED source is distributed throughout the optical medium. Due to reflective and transmissive surfaces having micro-scale diffractive and/or refractive surface patterns, the distributed light is collected into a rectilinear output with relatively uniform intensity. But in addition to those technical considerations, the illumination component(s) need to be mass-manufacturable at a reasonable cost. These teachings further address that challenge in that embodiments detailed herein provide an illumination system and method for LED (or other light source) based projectors which is small, has high efficiency and good uniformity, and is further efficiently mass-producible and robust.
The closest known prior art is seen to be a total internal reflection TIR-collimator, such as that used in the Mitsubishi® PK-10 LED projector. A schematic drawing of that TIR collimator and an image of the same are shown respectively at FIGS. 1A-B. The outer diameter of this component is about 20 mm. One problem seen with such a TIR collimator is that it collects the light but it does not form an image of the source so a separate fly's eye lens is apparently necessary in order to render the output illumination uniform and rectangular instead of a circularly symmetric. That causes either (or both) loss of light or increase of system size by increasing the etendue of the beam.
Separately, the concentration of light from a diffuse light source is required for many applications. One good example is the concentration of solar radiation. In solar concentration some problems with prior art systems known to the inventor is that they are incapable of concentrating light with near the maximum concentration ratio, and they are physically large with respect to the power they deliver. Some renditions also require some optical surfaces to be in near proximity to the location where light is concentrated, which can cause severe problems when a maximum concentration ratio is used because that optical surface will be affected where the light has a very high intensity. Also, for prior art concentrators that are based on parabolic reflectors, the heating element is disposed above the parabolic mirrors, which is a difficult physical arrangement. Embodiments of this invention address these concerns in that the components described can be used to concentrate light with a concentration ratio close to the theoretical maximum, but without the above problems. Specifically, a solar concentrator according to the teachings below may exhibit an almost maximum possible concentration ratio, with no optical surfaces near the heating element, and with the heating element below the concentrator which enables the heating element to be in a fixed position so that only the concentrator needs to track the movement of the sun.
In other fields such as microscopy or the optical measurements field, certain applications require a bright spot of light. This also is an advantageous deployment of the embodiments detailed below.